Effects of radial transport on divertor power and particle flux widths under different operational regimes in EAST

A study of the effects of radial transport on the outer divertor particle and power flux widths (λ js and λq) is carried out using plasmas under different operational regimes in the Experimental Advanced Superconducting Tokamak (EAST). In the EAST experiments, the λ js values measured during the grassy intra- and inter-ELM phases are similar, and the averaged value of λ js during grassy ELMy discharges is found to be smaller than that of the intra-ELM phase of type-I ELMy discharges but larger than that of the inter-ELM phase of type-I ELMy discharges. Simulations of scans of the radial particle and heat transport coefficients, D and χe, performed using the BOUT++ transport code show that both λq and λjs increase with D and χe, especially when D or χe is larger than a threshold value, indicating that background turbulence starts to matter in the determination of λq and λjs when D or χe surpasses the threshold value. A comparison between the simulation of theD scan and the experimental results shows that the different values of λ js obtained under different plasma operational regimes are probably due to the different intensities of background turbulence, which is beyond the scope of Goldston’s heuristic drift-based model as reported by Goldston et al (2012 Nucl. Fusion 52 013009), since their model was derived by assuming that turbulent transport does not exceed a certain level. The ratio of λ js to λq is greatly affected by the radial transport; however, simulations carried out using Scrape-off Layer Plasma Simulation (SOLPS) show that divertor geometry and plasma density have big influences on λ js, and thus could also affect the ratio of λ js to λq